The instant invention relates to electrophotocopiers having chain driven, reciprocating carriages for supporting an original document to be scan exposed, and more particularly to a camming yoke for coupling the reciprocating carriage to its drive chain.
In many electrophotocopiers marketed today, a reciprocating carriage is employed in order to scan expose an original document supported thereon. The reciprocating carriage is typically driven by a constant speed chain rotably supported by two sprockets disposed one near each end of the path of the reciprocating carriage. A T-shaped yoke is coupled to the carriage and a drive pin is coupled to the drive chain and vertically movable inside a vertical slot in the yoke. See, for example, U.S. Pat. No. 3,512,866, issued May 19, 1970. In this situation, the stroke of the reciprocating carriage is identical in length to the distance between the two sprockets supporting the drive chain. It is generally desirable to minimize the stroke of the carriage in order to minimize the space requirements for the copier, to increase the stability of the carriage, and to minimize the likelihood of the carriage becoming jammed. However, the length of the drive chain and the distance between the sprockets supporting the drive chain are generally determined by other parameters of machine design, such as synchronization with the photoreceptor belt, and thus cannot be reduced as a means of reducing the stroke of the carriage.
In reciprocating carriage type photocopiers, frequently when a maximum length copy is being made, the platen, in the course of its stroke, will completely pass over the transparent, exposure window, thereby allowing illumination from the photocopier to directly impinge on the operator. A shutter is employed in the copier to obviate this problem. In such case, it is desirable to shorten the stroke of the reciprocating carriage to be able to eliminate the need for a shutter.
The foregoing problems are overcome by the instant invention which provides a unique camming yoke and safety device for coupling the reciprocating carriage to the drive chain so that the stroke of the reciprocating carriage becomes less than the distance between the sprockets supporting the drive chain.